Note: Descriptions are shown in the official language in which they were submitted.
WO 2021/058995
PCT/1B2019/058026
1
Description
Title: Integrated motor-compressor unit having a cooling
circuit and a depressurization system configured to reduce
pressure of the cooling fluid
Background
[1] The field of the invention relates to integrated motor-compressor units
for
processing a working fluid, and more particularly to an integrated motor-
compressor having a cooling system.
[2] Generally, a motor-compressor unit comprises a centrifugal compressor and
a
motor integrated in a common housing.
[3] A centrifugal compressor with multiple compression stages generally
comprises
a plurality of impellers supported by a driven shaft coupled to a rotor driven
by
a motor or a turbine in order to generate a flow of compressed process gas.
[4] The shaft used to directly drive such a centrifugal compressor is required
to
rotate at relatively high speeds which generate heat. Furthermore, operating
the motor-compressor at high speeds increases windage frictional losses
resulting from components operating in pressurized gas.
[5] If this heat is not properly dissipated, it may negatively affect the
performance
of the motor, as well as damage the electrical insulation of the stator.
Increased
temperatures can also adversely affect the rotor-bearing systems of both the
compressor and motor, thus leading to bearing damage and/or failure.
[6] In order to regulate the heat and cool such an integrated motor-compressor
unit,
it is known to use a cooling circuit which may be an open loop cooling circuit
or
a quasi-closed loop cooling circuit where gas is drawn from the process stream
at some point in the compression process. The process gas is then circulated
through the motor and the bearings to absorb heat.
[7] For example, only a small amount of process gas is fed into the cooling
circuit
from the process stream. The cooling gas may be driven by a pressure
difference
between the source of the cooling gas and the place where the gas is allowed
to
flow to.
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[8] Alternatively, it is known to use a blower located before the cooling loop
to
circulate the cooling gas in said cooling circuit and thus improve the fan
compression efficiency. However, such solution increases significantly the
windage losses, even more when the machine works at high pressure.
[9] Reference can be made to document US 9, 200, 643 ¨ B2 which describes a
system for cooling a motor-compression with a closed-loop cooling circuit.
However, the motor is sealed from the compressor processed gas by dry gas seal
or carbon rings in order to avoid contamination, which increases the
maintenance of the seals.
lo Brief Description of Invention
[10]
One benefit afforded by
embodiments of the integrated motor-compressor
unit described herein is to reduce windage losses.
111] Indeed, the high speed motor, the coupling and the bearings being
immerged in the process gas, windage losses may be high, especially for
compressors with high suction pressure.
112] It is therefore proposed a depressurization system for an integrated
motor-
compressor unit having a motor and a compressor coupled to said motor. The
depressurization system is configured to depressurize the pressure of the
motor.
[13]
It is further proposed an
integrated motor-compressor unit configured to
process a working fluid, such as for example gas, and comprising a motor and a
compressor coupled to said motor via a rotatable shaft and mounted in a single
common housing, a cooling fluid is circulated throughout said housing in a
cooling circuit.
Summary
[14]
The integrated motor-compressor unit comprises
a depressurization system
configured to depressurize the pressure of the motor.
[15] The depressurization system is thus configured to reduce pressure of
the
cooling fluid circulating in the cooling circuit.
[16] Such a depressurization system creates a significant pressure drop of
at
least 10 bars. The efficiency of the motor is thus significantly increased.
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[17]
According to an embodiment,
the depressurization system comprises an
expansion device, for example before the cooling circuit, and an auxiliary
compressor, for example, after the cooling circuit, configured to recover the
suction pressure.
[18]
The expansion device may be, for example, a
cooling expansion valve
configured to receive the working fluid via a main compressor suction inlet of
the compressor and to transmit expanded cooled fluid to the cooling circuit,
and
the auxiliary compressor may be configured to receive the cooling fluid after
having cooled notably the motor and/or the bearings and to compress the
cooling fluid.
[19] According to another embodiment, the expansion device is an expansion
wheel.
[20] The expansion wheel may be mounted in various suitable locations
further
described and claimed herein.
121]
In an embodiment of operation of the
integrated motor-compressor unit the
motor rotates the shaft and thereby drives the compressor. A process gas to be
compressed is introduced via a main compressor suction inlet provided in the
housing. The compressor then compresses the process gas through successive
stages of impellers to thereby produce a compressed process gas. The
compressed process gas then exits the compressor via a process discharge
outlet
provided in the housing.
Brief Description of the Drawings
122]
Other aims, features and
advantages of embodiments of the invention will
become apparent on reading the following description, given purely as a non-
limiting example, and with reference to the attached drawings in which:
- Figure 1 very schematically represents an integrated motor-compressor
unit
according to a first embodiment of the invention;
- Figure 2 very schematically represents an integrated motor-compressor
unit
according to a second embodiment of the invention;
- Figure 3 very schematically represents an integrated motor-compressor unit
according to a third embodiment of the invention; and
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- Figure 4 very schematically represents an integrated motor-compressor unit
according to a fourth embodiment of the invention.
Detailed description
[231
The Figures very schematically
illustrate an integrated motor-compressor
unit 10 configured to process a working fluid, such as gas. The integrated
motor-
compressor unit 10 comprises a motor 12 and a compressor 14 coupled to said
motor 12 via a rotatable shaft 16 and mounted in a single common housing 18
configured to circulate a cooling fluid in a cooling circuit 27.
[24] The integrated motor-compressor unit 10 further comprises a
depressurization system 30 configured to depressurize the pressure of the
motor
12 and thus configured to reduce pressure of the cooling circulating in the
cooling circuit.
[25] Such a depressurization system 30 creates a significant pressure drop
of at
least 10 bars. The efficiency of the motor 12 is thus significantly increased
thanks to such pressure drop.
[26] The shaft extends substantially the whole length of the housing 18 and
comprises a motor section 17 coupled to the motor 12 and a driven section 19
coupled to the compressor 14. The motor section 17 and the driven section 19
of the rotatable shaft 16 are connected via a coupling 20, such as for example
a
flexible or rigid coupling.
[27] As illustrated, the motor section 17 and the driven section 19 are
supported
at each end, respectively, by one or more radial bearings 22. As way of a non-
!imitative example, four sets of radial bearings 22 are shown. The bearings 22
may be directly or indirectly supported by the housing 18.
[28]
The motor 12 may be an electric motor, such as
a permanent magnet motor
having permanent magnets mounted on the rotor (not depicted on the figures)
and a stator (not depicted on the figures). As an alternative, other types of
electric motors, such as for example synchronous, induction, brushed DC
motors,
etc... may be used.
[29]
The compressor 14 may be a multi-stage
centrifugal compressor with one or
more compressor stage impellers (not shown).
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[30] In order to cool or otherwise regulate the temperature of the motor 12
and
the bearings 22, a cooling gas is circulated throughout the housing 18 in the
cooling circuit 27 having cooling conducts 28 and hot conducts 29.
[31] The depressurization system 30 comprises an expansion device 32 before
5
the cooling circuit 27 and an auxiliary
compressor 34 after the cooling circuit 27
configured to recover the suction pressure.
[32] A first embodiment of the depressurization system 30 is shown on
Figure 1.
In this embodiment, the expansion device 32 is a cooling expansion valve
receiving process gas via the main compressor suction inlet 24 and
transmitting
expanded cooled process gas to the cooling circuit 27. The auxiliary
compressor
34 receives the cooling fluid after having cooled the bearings 22 and the
motor
12 and compresses it before transmitting to the main compressor suction inlet
24.
[33] The embodiment of Figure 2, where the same elements bear the same
reference differs from the embodiment of Figure 1 by the structure of the
expansion device 32. In this embodiment, the expansion device 32 is an
expansion wheel mounted on the motor shaft end. Alternatively, the expansion
wheel may be mounted on the compressor shaft end, between bearings or on a
dedicated turbo-expander. The auxiliary compressor 34 is, in this embodiment,
mounted on the compressor shaft end. Alternatively, the auxiliary compressor
34 may be mounted on the motor shaft end, between bearings, on a dedicated
turbo-expander, or on a dedicated compressor.
[34] The embodiment of Figure 3, where the same elements bear the same
reference differs from the embodiment of Figure 1 by the structure of the
expansion device 32. In this embodiment, the expansion is created by voluntary
compressor 14 leakages that are compressed by the auxiliary compressor 34. In
other words, calibrated gas leakages on the compressor end 14 are used to
generate the cooling flow. In this embodiment, and as a non-limitative
example,
the auxiliary compressor 34 is mounted on the motor shaft end.
[35]
The embodiment of Figure 4, where the same
elements bear the same
reference differs from the embodiment of Figure 1 by the structure of the
depressurization system 30. In this embodiment, the depressurization system 30
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comprises a blower device 36 mounted upstream the compressor 14 and
configured to circulate the cooling fluid in a closed loop cooling circuit 27.
The
depressurization system 30 further comprises a depressurization auxiliary
compressor 34 configured to compensate for the main compressor gas leakages.
The depressurization system 30 also comprises a cooler 38 mounted on the
cooling circuit 27 after the blower device 36.
[36] The depressurization auxiliary compressor 34 may be a low pressure
compressor or a dedicated equipment.
[37] In an embodiment of operation of the integrated motor-compressor unit
10,
the motor 12 rotates the shaft 16 and thereby drives the compressor 14. A
process gas to be compressed is introduced via a main compressor suction inlet
24 provided in the housing 18. The compressor 14 then compresses the process
gas through successive stages of impellers to thereby produce a compressed
process gas. The compressed process gas then exits the compressor 14 via a
process discharge outlet 26 provided in the housing 18.
[38] Thanks to the depressurization system of the invention, windage losses
are
reduced in the integrated motor-compressor unit, especially in compressors
having high suction pressure.
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